<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="app"></div>
  <template id="my-app">
    <h2>{{count}}</h2>
    <h1 v-once>{{count}}</h1>

    <button @click="add">+1</button>
  </template>


  <script src="https://unpkg.com/vue@3/dist/vue.global.js"></script>
  <script>
    const App = {
      template: '#my-app',
      data() {
        return {
          count: 100
        }
      },
      methods: {
        add() {
          this.count++;
        }
      }
    }
    Vue.createApp(App).mount('#app')
  </script>
</body>
</html>